Glycogen phosphorylase (EC 2.4.1.1) is a regulatory enzyme whose activity is modulated by a complex mechanism which includes activation by AMP and inhibition by glucose-6-phosphate. An understanding of the interaction between AMP, glucose-6-phosphate, or glucose-1-phosphate and the amino acid residues forming the respective binding sites may shed light on the mechanism of control at a molecular level. The goals of the project are to prepare and characterize nondissociable substrate activator-, or inhibitor-enzyme complexes by using photoactivatable analogs of the natural substrate and effectors. An azido derivative of AMP, 8-azido-AMP, will be tested as an affinity- label for the AMP binding site. An attempt will be made to synthesize azido derivatives of glucose following procedures similar to those described by Barker et al. or Saman et al. Optimum conditions will be established for the incorporation of approximately one mole of analog per mole of phosphorylase monomer. The modified enzyme will be extensively characterized by enzymatic and physical methods and compared to native phosphorylase. Finally, if sufficient evidence indicates that the analogs are covalently incorporated into the protein at or near the binding site for the normal effectors, the derivatives will be analyzed chemically. Peptides containing the bound analogs will be isolated and sequenced by standard procedures.